Diffusers are employed in compressors to convert what may be referred to as a "velocity head" to a "pressure head". It is, of course, highly desirable that this conversion be made with minimal losses since such losses reduce the efficiency of the operation of the machine employing the compressor.
One means of cutting diffuser losses resides in employing a so-called cascade diffuser wherein the vanes are arranged in two or more stages. The vanes in the first stage are located radially inward of the vanes in the second stage with the latter also being downstream of the former in the direction of air flow in the diffuser. Examples of this approach may be found in U.S. Pat. Nos. 3,588,270 issued June 28, 1971 to Boeics and 3,861,826 issued Jan. 21, 1975 to Dean as well as Paper No. 72-GT-39 published by the American Society of Mechanical Engineers and authored by R. C. Pampreen.
Even though these cascade diffusers reduce losses, because transonic velocity occurs in such diffusers, undesirable shock waves may be generated which create losses and otherwise detract from diffuser performance.
The present invention is directed to overcoming the above problem.